Spectrophotometric apparatus



April 26, 1955 R. LEE ETAL sPEcTRoPHoToMETRIc APPARATUS Filed Jan. 6,1951 /NvENToRS N O Y Em R L .mo LM W mnh/mu pmu..

SPECTRPHOTOMETRIC APPARATUS Royal Lee, Elm Grove, and William A. Hanson,Fox

Point, Wis., assignors to Lee Foundation for Nutritional Research,Milwaukee, Wis., a corporation of Wisconsin Application .anuary 6, 1951,Serial No. 204,808

2 Claims. (Cl. 38-1) The present invention relates to apparatus adaptedfor use in emission spectroscopy.

An object of the invention is to provide an improved spectrophotometricapparatus of the emission type including means for integrating oraveraging a selected spectral intensity over a short period to determinethe concentration of an element in a sample under investigation.

Another object is to provide spectrophotometric apparatus includingmeans for expeditiously making a graphic record of the spectralintensity.

Still another object is to provide a spectrophotometric apparatus whichincludes an improved form of llametype radiation source.

The invention further consists in the several features hereinafterdescribed and claimed.

In the accompanying drawing,

Fig. l is a diagrammatic view of a spectrophotometric apparatus arrangedin accordance with the invention, and

Fig. 2 is a sectional detail view of an emission device for theapparatus, taken generally on the line 2-2 of Fig. l.

In the drawing, 19 designates generally a radiation source or emissiondevice, hereinafter more fully described, in which a sample substance isto be burned. The light emitted by the ilame in which the samplesubstance is burned is passed into a suitable light filter ormonochromator 11, preferably adjustable, and including the usualcollimator 12. The segregated light leaving the monochromator isincident on a photo-sensitive device 13, such as a photo-emissive vacuumphoto-tube, which in some instances may be an electron multiplier tube.The photo-sensitive device is electrically connected to a suitableamplifier 14, such as of the D.C. type, the output tube of which isconnected to integrating means here shown to comprise a condenser 16which is discharged selectively through a ballistic galvanometer 17 or astylus-actuating coil 1S of a recorder 19. The recorder may be of anysuitable type and is here shown to carry a moving tape or strip 20cooperating with a recording stylus 21. The throw of the galvanometer,or the area under the curve 22 scribed on the record strip 20 to oneside of a longitudinal base line Z2', is a measure of the relativeintensity of the segregated light, and hence a measure of theconcentration of the element present in the sample.

The radiation source or emission device 10 comprises a verticalheat-resisting tube 23, such as' of quartz, transparent to the radiationunder investigation. The tube 23 is mounted on a base plate 24 having aninsulating pillar 25 on which is pivotally mounted a cover plate 26 forthe upper end of the tube, thus forming a combustion chamber 27 withinthe tube. The base plate and cover plate, of metal or heat-resistinginsulation, have respective sets of perforations 28 and 29 at the endsof the quartz tube. An inlet fitting 30 is secured to the bottom of theperforated base plate 24 and is connected to a conK duit 31 forsupplying oxygen to the combustion chamber, the conduit having a controlvalve 32 with one or more valve members 33, such as of the push-buttontype. The emission device is provided with ignition means, here shown tobe of the spark type. The base plate and cover plate form opposedhigh-voltage ignition electrodes and are preferably provided withprojections 34 and 35 forming electrode tips. The electrodes areconnected to the secondary winding of an induction coil or transformer36, the primary of which is connected to a supply circuit 37 2,705,923Patented Apr. 26, 1955 through a switch 38. The switch is closed as bymeans of a manually operable plunger 39 which also actuates a lever 40engaging one of the valve members 33 of the oxygen control valve, so asto open the control valve in advance of the closing of the switch 38. lnsome instances a reflector 41 is mounted behind the quartz tube 23.

The sample to be investigated, such as a small predetermined quantity ofblood or other biological material, is deposited and dried on a carrier42 of combustible material. The carrier preferably comprises apredetermined quantity of ashiess and spectroscopically pure cotton orfilter paper, which is placed in the combustion chamber 27. Thecombustible carrier is here shown to be in the form of a sheet whichextends longitudinally in the quartz tube. It may be desired, forexample, to determine the calcium content of the blood sample withrespect to a standard, as hereinafter described. Oxygen is admitted tothe combustion chamber, and the sample carrier is ignited by passing anelectric discharge between the electrodes. The burning period isrelatively short, preferably not more than about lone second. In someinstances, the carrier may be impregnated with a suitable oxidizingmaterial, such as potassium chlorate. However, it will be necessary toavoid interference with the segregated radiation of the sample. Thecarrier should be spectroscopically pure, at least with respect to theregion of the characteristic radiation of the sample.

The monochromator is adjusted to pass a desired narrow band of thespectrum, such as a band containing one or both of the spectral lines3833.7A and 3968.5A in the case of calcium. In some cases, two moremonochromators may be used to pass different spectral lines, the lighttherefrom preferably being incident on the same photocell.

The segregated light incident on the photocell 13 is amplied by the D.C.amplifier 14 which has a suitably regulated plate supply circuit 43 withpositive and negative terminals and with an on-off switch 44. The outputtube 15 has a load resistor 45 connected to the positive terminal of theplate supply. One terminal of the integrating condenser 16 is connectedto the anode of a diode or rectifier 46 the cathode of which isconnected to the plate or anode of the output tube. The other terminalof the condenser is connected to a point of positive potential on theplate supply which is approximately equal to the potential of the outputtube anode under quiescent conditions. By way of example, the platesupply is here shown to have a tapped voltage dividing resistor 47 forproviding various points of different potential.

The condenser terminals are connected by a pair of conductors 48 to aswitch 49, such as of the slide or wiping type, which automaticallyshort-circuits the condenser at a moment immediately preceding theignition of the sample carrier, so as to insure removal of any charge onthe condenser. The switch 49 is here shown to be operable by the plunger39 which actuates the oxygen valve 32 and the ignition switch 38. lfdesired, another switch 49 may be provided for short-circuiting thecondenser independently of the switch 49.

The integrating condenser 16 is also connected by a pair of conductors50 and 51 to the ballistic galvanometer 17, the conductor 5E) includinga discharge switch S2 and a selector switch 53. The capacity of theintegrating condenser is so selected that it will not ll during themaximum time cycle, such as 30 seconds. The throw of the galvanometer isa measure of the concentration of the element under investigation, andmay be compared with the throw produced by the combustion of one or morestandards.

The condenser is further connected by a pair of conductors' 54 and 55 tothe stylus-actuating coil 18 of the tape recorder 19. The conductor 54is connected to the conductor 5t) at a point between the switches 52 and53, and has a selector switch 56. The conductor 5S forms a branch of theconductor 51.

The recorder tape or strip 20 is pulled at a suitable constant speed, asby an electric motor 57 driving one of a pair of feed rolls 58 and 59between which the tape is engaged. The stylus 21 resting on the tapewill draw thereon the straight longitudinal base line 22 in the synapsesabsence of an actuating impulse. The recorder motor 57 is connected tosupply conductors 6d one ot' which includes a switch 6i and in someinstances a second seriesconnected switch 62. The switch 61 is actuatedsimultaneousiy with the condenser-d'ischarging switch 52, as by aconnecting link 63. However, the switch 61 closes before the switch 52so as to start the record tape in motion shortly before the switch 52closes. The switch 62 is arranged to energize the motor independently ofthe switch 61.

The area under the sample curve 22, which represents an integral of thespectral intensity with respect to time, can be measured, as bysquare-counting, or by a planimeter orotherwise. so that this area maybe compared with one or more reference areas corresponding to knownblood calcium concentrations. Another method of procedure consists incomparing the sample curve with a standard curve 1.22 drawn from a baseline 122 on a sheetV 12. The sheet may be transparent or translucent soas to permit superimposition on the sample curve. The standard curve 122is obtained in the same manner as the sample curve.

In the use of the apparatus, assuming that a tape record is to be made,the selector switch 55 is closed and the elector switch 53 is open. Thecover 26 of the emission device 1t) is opened and the impregnated samplecarrier 42 is placed in the combustion chamber 27, The monochromator isadjusted to pass the selected spectral line or lines of the samplesubstance. The plunger 39 is then depressed for a part of its stroke,opening the oxygen valve 32 to till the combustion chamber with oxygen,and also closing the switch 49 to short-circuit the integratingcondenser 16. The plunger is then depressed further to close theignition switch 3S, whereupon a spark will pass through the combustion.chamber and initiate combustion of the sample carrier. lt desired, theplunger may be partially released to discontinue the sparking as soon ascombustion starts, but the oxygen valve should remain open sutiicientlylong to effect complete combustion of the sample carrier. It is alsonecessary to remove thev short-circuit on the condenser before ignitionoccurs. The combustion period is relatively short, on the order of onesecond. The segregated light impulse incident on the photo-sensitivedevice is amplified by the D.C. amplilier 1.4, producing a voltagechange on the load resistor 4S, which results in charging of thecondenser 16 through the diode 46 to an extent depending on the spectralintensity and the period of combustion. The diode 46 prevents dischargeof the condenser through the load resistor and the output tube. Themotor switch 61 is then closed to start the recording tape in motion,and immediately thereafter the switch 52 is closed to discharge thecondenser through the stylus-actuating coil of the recorder, thusscribing the curve 22 on the record tape, as hereinbefore described. Assoon as the record curve is completed the switches 52 and 61 are opened.The curve 22 is then compared with reference areas or curves todetermine the concentration of the element in the sample, ashereinbefore explained.

When the ballistic galvanometer is to be used as the indicator, theprocedure is the same except that the switch 56 is open and the switch53 is closed, the throw of the galvanometer then being a measure of theconcentration of the element in the sample.

The size or weight of the combustible carrier sheets is not critical,provided that the element under investigation is dissipated in the flamebefore the end of the combustion period.

What we claim as new and desire to secure by Letters Patent is:

l. ln a spectrophotometric apparatus, a radiation source to which issubjected for a limited period a substance containing an element whoseconcentration is to be determined, whereby to excite said element, meansfor segregating from the radiation of the source a portion therentcharacteristic of the element, electronic means including a photocelland amplifier therefor for integrating in terms of an electrical chargethe intensity of the segregated light over the excitation period, saidamplifier having an output circuit including an integrating condenserfor storing the charge, and ballistic indicating means for translatingsaid electrical charge into a visual indication.

2. In a spectrophotometric apparatus, a radiation source adapted toexcite for a limited period an element contained in a sample, means forsegregating from the radiation of the source a portion thereofcharacteristic ot the element, a photo-sensitive device on which thesegregated light is incident and of a type producing an electricalimpulse proportional to light intensity, an electronic amplier foramplifying the electrical impulse and having an output circuitcontaining a load resistor the voltage across which varies with theelectrical impulse, an integrating condenser' in said output circuitnormally at zero potential diiierence and adapted to be charged byvariation of voltage acrossl the resistor, a rectiiier in series withthe condenser for permitting ow of charging current into said condenserbut preventing back flow, and current-actuated visual indicating meanshaving a circuit connection with said condenser, said circuit connectionbeing open during the condenser-charging period and being closed todischarge the charged condenser into said indicating means.

References Cited in the tile of this patent UNTED STATES PATENTS1,894,132 Stone Ian. 10, 1933 2,282,643 Cutting May 12, 1942 2,324,899Arthur July 20, 1943 2,344,719 Nusbaum et al Mar. 2l, 1944 2,346,512Schribner et al. Apr. 11, 1944 2,390,816 Suits Dec. 11, 1945 2,391,225Clark Dec. 18, 1945 2,420,077 Hasler et al May 6, 1947 2,436,104 Fisheret al. Feb. 17, 1948 2,509,649 Norman May 30, 1950 2,517,121 Liston Aug.1, 1950 2,527,122 Heigl et al. Oct. 24, 1950 2,577,814 Saunderson et alDec. 1l, 1951 2,577,815 Saunderson et al Dec. 11, 1951 2,597,001 latteMay 20, 1952 OTHER REFERENCES Gibb, Optical Methods of ChemicalAnalysis, first edition, published by McGraw-Hill Book Co., New YorkCity, 1942, page 8.

1. IN A SPECTROPHOTOMETRIC APPARATUS, A RADIATION SOURCE TO WHICH ISSUBJECTED FOR A LIMITED PERIOD A SUBSTANCE CONTAINING AN ELEMENT WHOSECONCENTRATION IS TO BE DETERMINED, WHEREBY TO EXCITE SAID ELEMENT, MEANSFOR SEGREGATING FROM THE RADIATION OF THE SOURCE A PORTION THEREOFCHARACTERISTIC OF THE ELEMENT, ELECTRONIC MEANS INCLUDING A PHOTOCELLAND AMPLIFIER THEREFOR FOR INTERGRAT-